Trichomycterus megantoni

biology_ecology

Ecology. Trichomycterus megantoni was collected in mountain rivers and streams that were generally 0.5 - 12 m wide and 0.3 - 1.5 m deep, with clear waters running over sandy, and rock-pebble substrates, at elevations of approximately 1,360 - 2,200 m. The water temperature ranged between 12 - 16 ° C, and the speeds of the current were moderate during the dry season. The environmental characteristics were similar to those observed for other Trichomycterus species in streams of Chile (Arratia, 1983 a) and in streams of northwestern Argentina (Fernandez & Vari, 2002).

A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Perú with comments on relationships within the genus.

description

Description. Morphometric data for holotype and paratypes given in Table 1. Elongated body, cylindrical; slightly compressed transversely in trunk region, becoming progressively more compressed towards the caudal fin. Dorsal and ventral profiles of trunk straight. Caudal peduncle profile straight. Greatest body depth at mid-trunk region, depth uniform posterior towards caudal fin. Caudal peduncle smoothly continuous with dorsal and ventral profiles of trunk. Papillae-like structures present on body. Anus located closer to anal-fin origin than to pelvic-fin insertion. Head rectangular in dorsal view. Eyes located on dorsal surface, ovoid. Skin covering the eyes thin and transparent, separated from the surface of the eyeball; orbital rim not free. Anterior naris slightly smaller than posterior naris, surrounded medially by fleshy flap of integument and laterally by barbels. Posterior naris partially surrounded anteriorly by flap of thin skin. Infraorbital canal discontinuous in two segments, bearing infraorbital pores 1 and 3, separated from posterior segment behind eye and bearing infraorbital pores 10 and 11. Supraorbital canal discontinuous with four pores: 1, 2, 3 and 6. Epiphyse

A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Perú with comments on relationships within the genus.

diagnosis

Diagnosis. Trichomycterus megantoni is readily distinguished from all other members of the subfamily Trichomycterinae from southern South America by having autapomorphic interopercle thickened integument (Fig. 2) and the presence of foramen frontal-supraoccipital reduced (Fig. 3). It is further distinguished from other congeners, with the exception of T. pseudosilvinichthys (Fernandez & Vari) and T. yuska (Fernandez & Schaefer), by the unique combination of the following features: tip of the pelvic fin when depressed not reaching the anus, premaxillae rectangle, first dorsal fin pterygiophore insertion at or posterior to vertebra 19 to 21, 17 or 19 pairs of ribs on each side, and 37 to 40 vertebrae. T. megantoni can be distinguished from T. yuska and T. pseudosilvinichthys by the presence of a supraorbital canal with pore 3, and an outer tooth row with conic teeth (versus absence pore 3 and distally narrowing incisiform teeth Fernandez & Schaefer, 2003; Fernandez & Vari, 2004). In addition, the new species is distinguished from T. yuska by head muscles that are not hypertrophied and 17 pairs of ribs on each side (versus head and cheek musculature hypertrophied and 18 or 19 ribs Fer

A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Perú with comments on relationships within the genus.

discussion

Discussion. Two probable autapomorphies were identified for T. megantoni. None of these can be definitely ascertained as unique within Trichomycterinae at this time, because some species are too rare to have their internal anatomy examined. The most peculiar features of T. megantoni are the interopercle thickened integument (Fig. 2) and frontal-supraoccipital foramen reduced (Fig. 3). The interopercle thickened integument ventrally on head, like an interopercular lobe of T. megantoni (Fig. 2) is unique among trichomycterines and possibly among trichomycterids. The condition differs from other species (Fernandez, 1999: Fig. 49 C, 133 B), where the interopercle lobe is absent and from basal trichomycterids such as the Copionodontinae (de Pinna, 1992: Fig. 2 B) and Trichogeninae. The most conspicuous feature in the skull of T. megantoni (Fig. 3) is the reduction of the frontal-supraoccipital foramen (= parietosupraoccipital Arratia, 1998). The plesiomorphic condition for the trichomycterids and catfishes in general is to have open cranial fontanels (de Pinna & Bristki, 1991). The cranial foramen of basal trichomycterids and other catfishes primitively extends though frontal and suprao

A new species of Trichomycterus (Siluriformes: Trichomycteridae) from the Andean Cordillera of Perú with comments on relationships within the genus.